The present disclosure relates generally to electrical interconnections for connecting printed circuit boards (“PCBs”) and more specifically to interconnection systems for carrying RF signals between printed circuit boards.
Electrical connectors are used in many electronic systems. It is generally easier and more cost effective to manufacture a system on several PCBs that are connected to one another by electrical connectors than to manufacture a system as a single assembly. A traditional arrangement for interconnecting several PCBs is to have one PCB serve as a backplane. Other PCBs, which are called daughter boards or daughter cards, are then connected through the backplane by electrical connectors.
Connectors in different formats are used, depending on the types or orientations of PCBs to be connected. Some connectors are right angle connectors, meaning that they are used to join two printed circuit boards that are mounted in an electronic system at a right angle to one another. Another type of connector is called a mezzanine connector. Such a connector is used to connect printed circuit boards that are parallel to one another.
Examples of mezzanine connectors may be found in: U.S. patent application Ser. No. 12/612,510, published as US-2011-0104948-A1; International Application No. PCT/US2009/005275, published as International Publication No. WO/2010/039188; U.S. Pat. No. 6,152,747; and U.S. Pat. No. 6,641,410. All of these patents and patent applications are assigned to the assignee of the present application and are hereby incorporated by reference in their entireties.
Electronic systems have generally become smaller, faster and functionally more complex. These changes mean that the number of circuits in a given area of an electronic system, along with the data rates, sometimes measured as bits per second or as a frequency, at which the circuits operate, have increased significantly in recent years. Current systems pass more data between printed circuit boards and require electrical connectors that are electrically capable of handling more data at higher speeds than connectors of even a few years ago.
One of the difficulties in making a high density, high speed data connector is that electrical conductors in the connector can be so close that there can be electrical interference between adjacent signal conductors. To reduce interference, and to otherwise provide desirable electrical properties, metal members are often placed between or around adjacent signal conductors. The metal acts as a shield to prevent signals carried on one conductor from creating “crosstalk” on another conductor. The metal also impacts the impedance of each conductor, which can further contribute to desirable electrical properties.
As data rates increase, there is a greater possibility of electrical noise being generated in the connector in forms such as reflections, crosstalk and electromagnetic radiation. Therefore, the electrical connectors are designed to limit crosstalk between different signal paths and to control the characteristic impedance of each signal path. Shield members are often placed adjacent the signal conductors for this purpose.
Crosstalk between different signal paths through a connector can be limited by arranging the various signal paths so that they are spaced further from each other and nearer to a shield, such as a grounded plate. Thus, the different signal paths tend to electromagnetically couple more to the shield and less with each other. For a given level of crosstalk, the signal paths can be placed closer together when sufficient electromagnetic coupling to the ground conductors is maintained.
Although shields for isolating conductors from one another are typically made from metal components, U.S. Pat. No. 6,709,294, which is assigned to the same assignee as the present application and is hereby incorporated by reference in its entirety, describes making an extension of a shield plate in a connector from conductive plastic.
In some connectors, shielding is provided by conductive members shaped and positioned specifically to provide shielding. These conductive members are designed to be connected to a reference potential, or ground, when mounted on a printed circuit board. Such connectors are said to have a dedicated ground system.
In some connectors, designed for high frequency signals, each signal conductor may be surrounded by shielding. This configuration provides an electrical configuration similar to what occurs in a coaxial cable in which a center conductor, carrying a signal, runs through a tubular grounded sleeve, and is sometimes referred to as a coaxial configuration. An example of such a connector may be found in U.S. patent application Ser. No. 13/170,616 which is an example of a board to board connector with a coaxial structure.
Other techniques may be used to control the performance of a connector. For example, transmitting data signals differentially can also reduce crosstalk. Differential signals are carried by a pair of conducting paths, called a “differential pair.” The voltage difference between the conductive paths represents the signal. In general, a differential pair is designed with preferential coupling between the conducting paths of the pair. For example, the two conducting paths of a differential pair may be arranged to run closer to each other than to adjacent signal paths in the connector. Conventionally, no shielding is desired between the conducting paths of the pair, but shielding may be used between differential pairs.
Examples of differential electrical connectors are shown in U.S. Pat. No. 6,293,827, U.S. Pat. No. 6,503,103, U.S. Pat. No. 6,776,659, and U.S. Pat. No. 7,163,421, all of which are assigned to the assignee of the present application and are hereby incorporated by reference in their entireties.
Electrical characteristics of a connector also may be controlled through the use of absorptive material. U.S. Pat. No. 6,786,771, which is assigned to the same assignee as the present application and which is hereby incorporated by reference in its entirety, describes the use of absorptive material to reduce unwanted resonances and improve connector performance, particularly at high speeds (for example, signal frequencies of 1 GHz or greater, particularly above 3 GHz). U.S. Pat. No. 7,371,117, U.S. Pat. No. 7,581,990, and U.S. patent application Ser. No. 13/029,052, published as US-2011-0230095-A1, which are assigned to the assignee of the present application and are hereby incorporated by reference in their entireties, describe the use of lossy material to improve connector performance.
Modern systems sometimes operate based on RF signals. RF signals might carry information representing video to be displayed or might carry information to an antenna for wireless transmission. Regardless of what information is carried by such a signal, passing RF signals through an interconnection system joining printed circuit boards can be challenging. The RF signals generally represent information in analog form, such that any distortion of the signal degrades the content of the information in the signal. In contrast, for a digital data signal, which at any given time represents a 1 or 0, so long as the noise or other distortion introduced into the signal is not so significant that it precludes a receiver from properly classifying the signal as a 1 or a 0, the noise has relatively little impact. The same amount of noise on an RF signal, however, might lead to perceptible distortion is the audio or video quality of the signal when it is rendered for a person or cause other undesired effects in a system using the RF signal.
To preserve the quality of an analog RF signal, it is known to make connectors to join printed circuit board to emulate a coaxial structure. Such connectors may be made of machined metal parts to provide a conductive ground structure surrounding a signal conductor throughout each RF signal path in the interconnection system.